Automotive catalytic converter technology has evolved in part with the replacement of two-way catalytic converter technology by three-way catalytic converter technology. A three-way catalytic converter receives its name from the fact that it is simultaneously capable of catalyzing three chemical reactions involved in the oxidoreductive removal of pollutants from a combustion exhaust stream. These three reactions, in general form, are: i) oxidation of unburned hydrocarbons to carbon dioxide, ii) oxidation of incompletely burned carbon monoxide to carbon dioxide, and iii) reduction of oxides of nitrogen (principally NO2 and NO) to nitrogen gas (N2).
Three-way catalysts currently employ a support structure such as cerium dioxide that is capable of storing oxygen for use when oxygen effluent in the exhaust stream is low. The cerium dioxide support can be doped with compounds such as oxides of aluminum or zirconium to improve thermal stability, surface area, and oxygen storage capacity. Catalytic centers which can be composed of noble metal cations (platinum, palladium, or rhodium) are incorporated into the support structure and can be direct mediators of emission gas oxidation/reduction.
While current catalysts exhibit promising features in terms of capacity, efficiency, and thermal stability, there is a constant need to find further improvements in order to meet ever more demanding regulatory requirements.